Let me start by admitting that cherry picking range is not directly relevant to building a commercial networks that must have deep reliable coverage. We cannot draw an 88 mile radius circle around one of our tower based Access Points and make the credible claim that by πr2,we can cover 24,000 square miles with a single tower. However, there is an indirect relevance in that the same aspect that allows RPMA to be used to build deep, reliable coverage (i.e. link budget) is the same aspect that allows for some truly amazing cherry picked results. Other technologies advertise their cherry pick, so we will play that game and show you quite an amazing cherry in the process.
What we would like to explore in this post is how to efficiently send very small packets of data. For this post, we’ll concentrate on the uplink. Stay tuned for a description of the RPMA downlink in a future post.
Part Nine: Power Consumption
Low Power Wide Area (LPWA) devices are often battery powered. After all, the LP of LPWA stands for “low power”. Given that these devices are low cost, they do not warrant the cost of frequent battery replacement. Requiring labor to service these types of devices destroys the Return on Investment (ROI) the connectivity. Battery life of 10-20+ years is critical.
Thus, power consumption is extremely important to optimize for maximum battery life. Power consumption is an unknown until a finalized production system and endpoints are commercially available in the field. Cellular LPWA is designing the protocols with power consumption in mind, but they are years away from proving out the actual real-world measurements on a commercial system and have fundamental design issues regarding power consumption that will become apparent over time.
Power consumption is an unknown until a finalized production system and endpoints are commercially available in the field.
Part Eight: Robustness
Robustness (or the lack thereof) in the cellular LPWA specifications is another example of cellular folks being clever to specify requirements that are easily achievable. In this case, its simulation based on the TU-1 Hz channel model as stated in TR45.820 : Cellular system support for ultra-low complexity and low throughput Internet of Things (CIOT) lacks realistic expectations. RPMA has been in field deployed for 6 years and we have routinely seen channels in the field that are far more adversarial. We were surprised at the variability of the channel even for stationary devices.
The Typical Urban(TU) 1 Hz channel model is not a realistic model even for stationary devices, yet that is the channel model that governs all of the cellular LPWA simulations.
Part Seven: Firmware Download
Being able to download firmware updates is a critical capability in virtually all applications we have encountered. 10-20 years is a long time to commit to a factory installed firmware image. This is another example of where the cellular folks were smart enough to bias the requirements inTR45.820 : Cellular system support for ultra-low complexity and low throughput Internet of Things (CIOT). The problem is that the requirement governing code download size is far from realistic.
Part Six: Downlink Capacity
Even though LPWA tends to consist of uplink centric data models, downlink capacity looms as a potential bottleneck for the following reasons:
- As we saw in the Part 5, there is downlink control required for scheduling uplink transmissions and acknowledging uplink transmissions (especially for frequent small packet communication).
- Based on the enhanced link budgets of LPWA approaches, the supported downlink rates of the channel is far lower which exacerbates the downlink bottleneck.
- The amount of downlink power available for cellular LPWA is severely limited. Less power means less capacity. The LPWA cellular is either adjacent to voice/data channels or is contemplated to be in the stop-band. In either case, transmit power must be minimized to the point of not interfering with voice/data communication – the cash-cow of the industry. This is yet another example of all technical decisions being driven (understandably) by voice/data needs at the expense of the machines.
…limiting the ability to acknowledge transmissions would be very disappointing to the applications that plan on using the cellular LPWA network. Reliable delivery is a crucial requirement for LPWA devices.
Part Five: Uplink Capacity
Uplink capacity is crucial to how many devices can be supported per base station. We agree with the cellular industry’s assessment that the numbers can be very high. 3GPP predicts as high as 40 devices per household. Cellular LPWA claims to be able to support these devices, but they seem to impose some rather unpleasant constraints on the data model. As the requirements laid out in the 3GPP document, TR45.820 : Cellular system support for ultra-low complexity and low throughput Internet of Things (CIOT), endpoint data is assumed to be buffered over long periods of time and sent infrequently to achieve sufficiently high capacity for LPWA. For a number of reasons, this greatly limits the usefulness of the cellular LPWA system.
Fundamental Cellular Issues
There are two fundamental issues when it comes to uplink capacity.
Part Four: Cellular LPWA Complexity
Simplicity is critical for the IOT devices. Imagine integrating a low-cost communication module in an appliance at any factory in the world, and having simple, ubiquitous, out-of-the-box connectivity enabled in any other part of the world. This vision is certainly not enabled by the cellular LPWA approaches like NB-IOT, LTE-M, or EC-GSM. Cellular will require support of 30+ bands and the expense of 100+ carrier certifications for worldwide coverage. RPMA, by contrast, is one simple 2.4 GHz band and one low-impact certification process.
Part Three: 3GPP/GSMA is NOT Providing a Graceful Evolution Path for Machines
The 3GPP/GSMA folks may claim that their roadmap offers “graceful evolution” for machines, but we do not have to look far into the past to see that this has never been the case, and likely never will be the case. Let’s look at three categories of issues that run counter to a “graceful evaluation” and destroys the Return-On-Investment (ROI) of low-end machines: Sunsetting Risk, Fragmentation, and Machine Priority.
Part Two: Cellular LPWA Availability
There are lots of pilots being announced within 3GPP/GSMA so isn’t commercial service imminent? The short answer is no. Pilots, as defined in this industry, are a short-circuit of the process. The original Nuel/Huawei “clean-slate” proposal (which is now defunct) had a number of pilots. Clearly, that was not on the path of offering a commercial service.
Despite vendor’s and cellular carriers’ claims that service is imminent for cellular, these systems are years away from a commercial offering. Standards and minimum performance specifications must be finalized, silicon and nodes must be productized, certification programs developed, and ecosystems must be built.
By contrast, RPMA technology is available today.